Electro-formed ring interconnection system

ABSTRACT

Multiple small conductive and flexible hollow rings, each of which is made from a pliable material, provide a flexible connection medium for use between a substrate and a microelectronic device package. Each ring is soldered to both the substrate and the device and held in place during manufacture by way of a flexible non-conductive film in which H-shaped cutouts are formed and into which a conductive ring is inserted. The interior sections of the H-shaped cutouts extend into the conductive rings and hold the rings in place during manufacture. A portion of the sidewall of each ring is not soldered thus insuring that at least part of the ring stays flexible. The rings accommodate elevation differences on a substrate and electronic device package. They also provide a vibration resistant and flexible joint.

REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. provisional patentapplication Nos. 60/575,347 and 60/575,348, both of which were filed May28, 2004.

BACKGROUND OF THE INVENTION

The present invention relates generally to high-density electricalinterconnections structures and more particularly to such aninterconnection structure that may be used in interposer applicationsand to connect electrical devices to circuit boards.

Microelectronic devices such as state-of-the-art microprocessors requirelarge numbers of reliable connections in increasingly-small areas. Asthe number of connections between an electronic device and a substrateto which the device is to be mounted increases, the likelihood that justa single connections will not be made or will fail increases.

In “wave soldering,” an electronic components is soldered to a substrateby flowing molten solder over a substrate in which electronic componentsare mounted. A substrate, to which electronic components are to besoldered, is passed over the flowing, molten solder such that exposedmetal and fluxed surfaces on the lower surface of the substrate surfacewick the molten solder upward from the solder bath. As the substratewith the wicked, molten solder moves away from the molten solder bath,the solder cools and solidifies, establishing an electrical connectionbetween electronic devices and soldered surfaces of the substrate.

As connection density increases in the electronic arts and lead lengthsfrom electronic devices decreases, the increasing number of connectionsthat must be made make it statistically more likely that even a singleconnection will not be made or will fail. Even minor irregularities in asubstrate's planarity can cause connection problems.

One problem with prior art soldering techniques arises when the contactsurfaces of a substrate and an electronic device are separated from eachother by different distances. For example, if one or two contact leadsor one or two contact surfaces of a microprocessor are more widelyseparated from a planar substrate than the other contact leads orcontact surfaces, the molten solder might not wick between the substrateand the more-distant contact surfaces of the electronic device. Priorart soldering techniques suffer from an inability to make a connectionwhen the spacing or distance between contact surfaces of two devices orsurfaces to be joined, varies by more than a small amount.

When even a single connection between an electronic device and itssupporting substrate is either not made at the time of manufacture, orfails while in use, the cost to identify a failed electrical connectionand to repair it can often exceed the cost to manufacture the product inwhich the electronic device and supporting substrate operates. Improvingthe manufacturability of electrical connections and improving thereliability of electrical connections after manufacture would be animprovement over the prior art.

The present invention is directed to a connector structure that issuitable for use in high-density applications, is easy to manufactureand which provides a reliable contact force while avoiding theaforementioned shortcomings.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a connectordevice that has a plurality of flexible, conductive rings arranged in anarray so as to contact conductive pads on a circuit board and contactsor contact pads of an opposing electronic device.

Microelectronic devices are electrically connected and mounted to acircuit board or other planar surface using small conductive hollowrings between electrical contacts of an electronic device and a circuitboard or substrate. Each ring is a band of pliant conductive materialthat extends around a center point. An axis of rotation extends througheach ring. Each ring's axis of rotation is substantially parallel to theother axes or rotation and to the plane of the substrate and the planeof the electronic device.

Each ring acts as a small, round spring-type of contact which willdeform when a force is directed toward the interior of the ring from anydirection. When the force is removed, the ring will return to itsoriginal shape. The resilient behavior of the rings provide a small,flexible interconnection which can accommodate variations in theplanarity of opposing surfaces. Each ring's flexibility alsoaccommodates circuit board or substrate flexing as well as impacts andvibration.

The rings are preferably electroformed. Electroforming permits verysmall rings to be formed and with diameters as small as 500 micrometers.During manufacturing of an electronic device to a substrate, the ringsare held in place by a flexible film carrier that is slit, cut orotherwise formed to remove material from the carrier in the shape of theletter “H.” A ring is passed “through” the H-shaped material opening inthe film carrier and then held in place by film carrier material thatextends through the ring's center. Several conductive rings can becarried by a single piece of film, which can then be used to positionthe rings (and the film carrier) between a substrate and an electronicdevice. The film carrier supports the rings in the manner of aninterposer without require any complex steps of molding the carrier. Thefilm carrier also may flex with or preferably does not offer anyinterference with the compression and expansion fo the rings.

These and other objects, features and advantages of the presentinvention will be clearly understood through a consideration of thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of this detailed description, the reference will befrequently made to the attached drawings in which:

FIG. 1 is a perspective view of a discrete conductive hollow ringconstructed in accordance with the principles of the present invention,and which is suitable for connecting an electronic device to a circuitboard or other substrate;

FIG. 1A shows the deformation of the discrete conductive hollow ring ofFIG. 1 in response to an externally-applied force;

FIG. 2 is a side elevation of a microelectronic device and a pluralityof conductive hollow mounting rings mounted to a substrate;

FIG. 3 is a side elevation of a conductive mounting ring filled with aresilient, non-conductive material and the ring being soldered to asubstrate;

FIG. 4 is a side elevation of a substrate and a plurality of conductivehollow mounting rings mounted to an electronic device; and,

FIG. 5 shows a conductive ring and the space between an electronicdevice and a substrate filled with non-conductive resilient material.

FIG. 6 is a perspective exploded view illustrating how a singleconductive hollow ring is aligned with an opening in a flexible filmcarrier prior to insertion of the ring in the opening;

FIG. 7 is an end view of FIG. 6;

FIG. 8 is the same view as FIG. 7, but with the conductive ringpartially inserted into the opening of the film carrier;

FIG. 9 is the same view as FIG. 8, but with the conductive ringcompletely inserted into the opening of the film carrier;

FIG. 10 is a perspective view illustrating the conductive ring in placewithin the film carrier; and,

FIG. 11 is an end view of a connector, or interposer, constructed inaccordance with the principles of the present invention illustrating aplurality of rings that are held in place between a substrate and anelectronic device by a film carrier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a perspective view of a discrete conductive hollow ring 10which is constructed in accordance with the principles of the presentinvention and which may be used for the mounting of an electronic deviceto a circuit board or other substrate. In the embodiment shown, theconductive hollow ring 10 has a diameter D substantially the same as thelength L of the ring 10, but other configurations may be used.

The ring is preferably made up of a band of pliant conductive material,such as a copper or gold alloy or a spring steel coated or plated with agood conductor such as copper or gold. Alternate embodiments can includeresilient plastics that are either plated or otherwise conductivelycoated. Regardless of its material, as is true of all rings, thematerial from which it is made is centered about a point in space 12through which extends an axis of rotation 14 for the ring 10. A force,F, exerted on the ring 10 from the exterior, and directed radiallyinward of the ring, will cause the ring 10 to deflect as shown in FIG.1A. As is well-known, as the force F increases past the material'selastic limit, the ring will collapse but as long as the applied force Fremains below the elastic limit of the ring material, the ring 10 willact as a spring, and return to its original shape when the applied forceis removed. The spring-like action of the ring 10, when used as in arrayof rings will provide a connection that can accommodate planaritydifferences between a substrate 8 and an electronic device 6. It canalso provide a connection that can be flexed and which will be moretolerant of impact and vibration. The improved physical robustness isprovided by the flexible material from which the ring 10 is made, aportion of which between the substrate 8 and device 4 is not soldered.

The ring 10 illustrated is provided with two strips, or bands, ofnickel-plating 20, 22 that run along the side of the ring 10 from oneopen end to the other. The nickel plating bands 20 and 22 act as and arereferred to herein as solder barriers 20 and 22. As shown, they aresubstantially opposite to each other on the exterior surface of the ring10. They prevent solder from wicking all the way up and around thecircumference of the ring, thereby insuring that at least part offlexible ring side wall will not be soldered to the substrate 8 or anopposing surface, but rather will still remain pliant.

As shown in FIG. 3, when the ring 10 is attached to a substrate 8,molten solder will only wick upwardly until it reaches the solderbarriers 20 and 22. Solder that wicks upward along the exterior of thering 10 will form fillets 24 between the ring's 10 lower curvature (FIG.10) and the top of the substrate 8 as part of the normal solderingprocess. The solder barriers 20 and 22 insure that flexible materialfrom which the ring 10 is made will not be completely coated with solderduring a soldering process, insuring that the ring 10 will retainflexibility.

In a preferred embodiment as shown in FIG. 1, the ring 10 side wallcross-section is substantially planar or rectangular. In an alternateembodiment, the ring side wall cross-section can be circular, oval orother shape although non-rectangular side wall shapes might tend to bemore rigid. Inasmuch as a circle and an oval are both special caseellipses, the more general side wall shape is referred to herein aselliptical.

FIG. 2 is a side elevation of a microelectronic device 4 positioned justabove a plurality of conductive hollow mounting rings 10, the assemblyof which comprise a connector 2 for mounting the electronic device 4 toa circuit board or other substantially planar substrate 8. Each of therings 10 in FIG. 2 is substantially the same as the ring 10 shown inFIG. 1 albeit in FIG. 2, the solder barriers 20 and 22 are not visible.

The mounting rings 10 in FIG. 2 are aligned to that each of their axes14 are parallel to each other and extending into the plane of thefigure. In an alternate embodiment, the rings 10 can have their axesco-linear.

Inasmuch as the axes 14 extend into the plane of FIG. 2, the axes 14 ofthe rings 10 also tend to extend parallel to the plane of the substrate8 which also extends into the plane of FIG. 2, as well as the plane ofthe underside 6 of the device 4. The side walls of each ring therefore“face” the substrate 8 and the underside 6 of the device 4. The planesin which the ring 10 open ends lie are substantially orthogonal to thesubstrate surface 8 and the underside 6 of the electronic device 4.

The several discrete conductive hollow rings 10 each provide a redundantsignal path along its body between conductive traces on the surface 8 ofthe substrate and connection points or nodes on the under side 6 of theelectronic device 4. Signals can traverse both sides of the ring to getfrom circuits on the device 4 to circuits on the substrate 8 below. Thisdual signal path also assist in reducing the inductance of the system inwhich such contacts are used. As shown in FIG. 2, the several conductiverings 10 are initially attached to the substrate 8 and provide aconnector for the device 4.

FIG. 3 shows an alternate embodiment of a conductive ring 10 wherein theinterior 18 of the ring 10 is filled with a resilient, non-conductivematerial 18, such as silicone. The aforementioned solder fillets 24mechanically and electrically attached the ring 10 to the substrate 8.Filling the interior 18 space with a resilient material increases thestrength of the ring 10 but also prevents solder from flowing into theinterior space 18 by either wicking or capillary action.

FIG. 4 shows a connector 2 for mounting an electronic device. In FIG. 4,the connector 2 is formed using the aforementioned discrete conductiverings 10, but the connector 2 in FIG. 4 includes a non-conductive underfill material 26 which holds the conductive rings 10 in place withrespect to each other. The under fill material 26 can be anon-conductive silicone layer, the thickness of which is less than theoutside diameter of the conductive rings 10. When the electronic device4 is urged downward, each of the rings will deform slightly. Becausethey are pliable, with each of them tending to oppose a downwardcompressive force, each conductive ring 10 will tend to make physicalcontact with the surface of the substrate 8 below it as well as thesurface 6 of the electronic device 4 above it. Each ring will thereforeprovide a better electrical and physical contact than is otherwisepossible with a straight pin used in the prior art.

FIG. 5 shows a non-conductive, resilient under fill material 26 disposedbetween the device 4 and a substrate. It also shows the hollowconductive ring 10 filled with the under fill material, adding stiffnessto the ring 10.

The connector 2 shown in FIG. 4 can be initially attached to thesubstrate 8 or to the electronic device 4. It can be wave soldered toeither the substrate 8, the device 4 or both of them simultaneously.

As shown in FIG. 2 and FIG. 3, each of the hollow contact rings 10 ofthe connector 2 shown in FIG. 4 has solder barriers (not shown in FIG.4) which prevent molten solder from wicking all the way around the ring10 thereby defeating the flexibility provided by the thin metal fromwhich the rings are made.

The hollow, conductive rings are preferably made from electronicallyconductive metals that will also accept a solder barrier. Copper, silverand gold are excellent conductors and can be alloyed with other metalsthat can provide good resilience; they can also be locally plated withsolder-barrier metals such as nickel. The rings 10 can also be formedfrom metal-plated plastics.

The hollow, conductive rings are preferably made from electronicallyconductive metals that will also accept a solder barrier. Copper, silverand gold are excellent conductors and can be alloyed with other metalsthat can provide good resilience; they can also be locally plated withsolder-barrier metals such as nickel. The rings 10 can also be formedfrom metal-plated plastics. In an alternate embodiment of the connector2 that is shown in FIG. 4, the hollow conductive rings 10 are held inplace with respect to each other by a resilient and flexible film(referred to hereafter simply as “flexible film”) that is provided withH-shaped cut-outs or slits through which a conductive ring 10 can bepassed. As the conductive ring 10 passes into an H-shaped cut, theresilient and flexible film material “inside” the “H” extends into thering, holding it in place.

FIG. 6 illustrates a single conductive hollow ring 10 of a multi-ringconnector 2 (not shown in FIG. 6 but shown in cross-section in FIG. 11).The ring 10 is shown as being positioned above a planar sheet ofnon-conductive flexible film 30 such as Kapton or the like. Thinplastics may also be used. The film 30 may be die-cut or laser-etched orotherwise formed so that the film material is selectively removed suchthat the removed material forms an opening in the shape of an “H.” InFIG. 6, this H-shaped cut is identified by reference numeral 32.

As can be seen in FIG. 6, the film material that is removed from thesheet to form the “H” opening leaves small, flap-like extensions of filmmaterial that form flaps of the “H” shape and which extend into thehollow interior of the ring, when assembled. The film material thatremains after the H-shaped cut or otherwise formed in the film 30 isidentified in FIG. 6 by reference numerals 34 and 36. Because theseflaps of film material 34 and 36 are free of the film 30 on three sides,they can also be considered to be cantilevered from the body of the film30 and opposing each other. If the film 30 is appropriately selected tobe appropriately resilient, the opposing flaps 34 and 36 will deflect“downward” when the ring 10 is pushed “into” the “H” thereby allowingthe ring 10 to be inserted into the film 30. As the ring 10 continuesthrough the film 30, its perimeter will clear the flaps 34 and 36,allowing them to spring back to their original position. The flaps 34and 36 will thereafter loosely hold the ring 10 in place by the flaps 34and 36 extending into the interior 18 of the ring 10.

Those of ordinary skill in the art should appreciate that the ability ofthe film 30 to fix the hollow conductive rings 10 in their designatedpositions will depend on the relative size of the rings and H-shapedopenings 32 with respect to each other. The conductive hollow rings 10and their H-shaped associated openings 32 are each preferably sized andshaped so that they can be cooperatively engaged to each other when theconductive hollow ring 10 is inserted and positioned in the H-shapedopening 32.

FIG. 7 shows a conductive hollow ring 10 positioned in alignment with anopening and disposed just above the opposing first and second flaps 34and 36 formed by the H-shaped opening 32. Each H-shaped opening includesa central base portion that interconnects two spaced-apart leg portions,which are preferably arranged parallel with each other. In FIG. 8, thering 10 is shown partially through the sheet of flexible film 30,deflecting the opposing first and second carrier flaps 34 and 36,downwardly. In FIG. 9, the conductive hollow ring 10 has been pushedinto the H-shaped opening 32, below the extent of the carrier flaps 34and 36 such that the flaps 34 and 36 cleared the circumference of thering 10 and returned to their original position, i.e., toward eachother. In FIG. 9 however, the carrier flaps 34 extended into theinterior 18 of the ring 10. The bodies of the conductive rings arealigned with the center base portions of the H-shaped openings.

FIG. 10 shows one of the rings 10 fully inserted into the H-shaped cut32 formed in a sheet of non-conductive flexible film 30. The carrierflaps 34 and 36 are shown extending into the interior 18 of the ring 10.

As can be seen in FIG. 10, the tightness of the ring 10 in the film 30will depend in part on the dimensions of the opening 32 and thethickness of the ring 10 material. The ring 10 can be held in place,relative to other rings (not shown) by the carrier flaps 34 and 36.

Finally, FIG. 11 shows a substantially planar substrate 8 to which amicroelectronic device 4 having a substantially planar bottom surface 6is electrically connected using a connector 2 formed from several,discrete hollow conductive rings 10 that are fixed in space using theaforementioned flexible non-conductive film 30. The device 4, substrate8 and connector 2 are all shown in cross-section. The rings 10 are heldin place during assembly of the device 4 to the substrate 8 by using theaforementioned sheet of non-conductive flexible film 30.

Like the substrate depicted in FIG. 4, the substrate 8 depicted in FIG.11 also has conductive traces that carry signals to and from the device4. The several discrete conductive hollow rings 10 each provide aflexible electrical connection between the traces on the substrate 8 andcontact points on the device 4. By orienting the “H”cuts (not shown inFIG. 11) the same way, each of the rings 10 can be oriented with theiraxes parallel to each other. Similarly, by rotating the “H” cuts, theorientation of the rings can be modified as desired. Or, the openings 32may be arranged within the film carrier in a radial pattern.

Those of skill in the art will recognize that the connector assemblyshown in FIG. 11 that is comprised of the film 20 its associatedplurality of conductive rings 10 can be attached to and be a part ofeither the substrate 8, the device 4. The connector assembly can also beused to connect the substrate 8 to the device 4 as its own separateconnector.

In the preferred embodiment, the flexible film 30 is embodied as apolyimide film. Those of ordinary skill in the materials art willrecognize that other flexible or resilient, non-conductive materials canbe used as well.

The rings 10 are preferably formed using an electroforming process,which is well known in the electronics art. Ring 10 dimensions as smallas 500 micrometers are possible although larger-dimensioned rings, e.g.,up to 1000 micrometers and beyond, are easier to handle for manyapplications. Alternate embodiments include using flexible plastic toform the rings. By coating the exterior surfaces with metal, plasticrings can be used as well.

As set forth above, the preferred embodiment also may utilize a solderbarrier on the exterior surfaces of the ring 10, which acts to stopmolten solder from wicking all the way around the ring 10. The solderbarrier for the connector 2 shown in FIG. 11 is a band of nickel on thering's exterior, located on the ring 10, substantially mid-way betweenthe bottom surface 6 of the device 4 and the substrate 8. Keeping themid-sections of the ring 10 free of solder helps to insure the ring'sflexibility.

Those of skill in the art will also appreciate that since each of therings 10 can be slightly compressed from their original shape so thatthe rings may overcome slight variations in the planarity of thesubstrate 8 and/or the electronic device 4. By providing a solderbarrier that prevents solder from wicking all the way around a ring, theside walls of each ring acts as a small round spring and will deformwhen a force is directed toward the interior of the ring. When the forceis removed, the ring will return to its original shape. The resilientbehavior of the rings provide a small, flexible interconnection whichcan accommodate variations in the planarity of opposing surfaces. Eachring's flexibility also accommodates circuit board or substrate flexingas well as impacts and vibration. Keeping several rings 10 in positionand alignment during manufacturing greatly improves themanufacturability of devices using the flexible rings 10 and increasesthe reliability of electronic devices. The resulting connection betweenthe substrate 8 and an electronic device 4 is more tolerant of substrateand/or device flexing. The connection is also less susceptible to shockor vibration-induced failure.

While the preferred embodiment of the invention have been shown anddescribed, it will be apparent to those skilled in the art that changesand modifications may be made therein without departing from the spiritof the invention, the scope of which is defined by the appended claims.

1. A connector for connecting an electronic device to a substrate, theconnector comprising: a sheet of non-conductive flexible film, the filmhaving a plurality of H-shaped openings formed therein, each of theopenings defining opposing first and second ring retention flaps formedin the film; a plurality of continuous, conductive hollow rings, each ofthe rings including a continuous body that extends completely around anaxis of rotation to define a hollow interior volume of said ring, eachof the rings enclosing a hollow volume, said rings being held upright insaid openings by the opening first and second retention flaps whichextend at least part way into said ring hollow interior volumes; and,each of said rings is provided with first and second solder barriers onexterior surfaces of said rings for inhibiting the wicking of moltensolder around circumferences of said rings during soldering of saidrings to a substrate, said first and second solder barriers are disposedopposite each other on said exterior surfaces of each of said rings. 2.The connector of claim 1, wherein said film is a polyimide film.
 3. Theconnector of claim 1, wherein each of said rings is electroformed frommetal.
 4. The connector of claim 1, wherein each of said rings areformed from a non-conductive material, and at least portions of exteriorsurfaces of said rings are coated with conductive material.
 5. Theconnector of claim 1, wherein the solder barriers include extents ofnickel disposed on said exterior surfaces of each of said rings.
 6. Theconnector of claim 1, wherein said rings have diameters that range frombetween approximately 500 micrometers and approximately 1500micrometers.